Electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

ABSTRACT

An electrode for a non-aqueous electrolyte secondary battery according to one embodiment includes a belt-like current collector, a mixture layer formed on each surface of the current collector, and a lead bonded to an exposed portion of the current collector where the surfaces of the current collector are exposed, the lead extending from one end of the current collector, the one end and another end constituting both ends of the current collector in the width direction. The mixture layer on at least one surface of the current collector is formed in the width direction of the current collector and adjacent to the exposed portion on the other end side, and the length in the width direction of a portion of the lead disposed on the current collector ranges from 60% to 98% of the width of the current collector.

TECHNICAL FIELD

The present disclosure relates to an electrode for a non-aqueouselectrolyte secondary battery and a non-aqueous electrolyte secondarybattery.

BACKGROUND ART

Non-aqueous electrolyte secondary batteries include a wound electrodeassembly manufactured by winding a positive electrode and a negativeelectrode with a separator interposed therebetween, for example. In thepositive electrode and the negative electrode constituting the woundelectrode assembly, typically, a mixture layer is formed on each surfaceof a belt-like current collector, and a lead is bonded to an exposedportion where the surfaces of the current collector are exposed. Inrecent years, electrodes with various structures have been proposed toimprove the battery performance, such as battery capacity or output. Forexample, Patent Literature 1 discloses an electrode in which an exposedportion to which a lead is to be bonded is formed on only one end sideof a current collector in the width direction to increase the area of amixture layer and thereby increase battery capacity. Patent Literature 2discloses an electrode in which an exposed portion is formed over thefull width of a current collector.

CITATION LIST Patent Literature

PTL 1: Japanese Published Unexamined Patent Application No. 2003-68271

PTL 2: Japanese Published Unexamined Patent Application No. 2008-234855

SUMMARY OF INVENTION Technical Problem

When an exposed portion is formed on only one end side of a currentcollector in the width direction, a lead is typically unevenly bonded toone end side of the current collector in the width direction. Becausethe lead has a larger thickness than a mixture layer, in a woundelectrode assembly including the electrode disclosed in PatentLiterature 1, the electrode assembly bulges locally on one end side inthe axial direction due to the large thickness of the lead. Thus, whensuch an electrode is used, it is difficult to form a stable windingstructure outside the lead bonded portion, and winding misalignment ofan electrode assembly is likely to occur.

Winding misalignment is reduced when an exposed portion is formed overthe full width of a current collector, as in the electrode disclosed inPatent Literature 2, and when a lead is bonded to a current collector soas not to be unevenly bonded to one end side of the current collector inthe width direction. In this case, however, an electrically conductiveforeign material may easily enter an electrode assembly through a frontedge of a lead disposed on a current collector, for example, in abattery manufacturing process, and the foreign material may cause adecrease in open-circuit voltage (OCV) or cause internal short-circuit.

Solution to Problem

An electrode for a non-aqueous electrolyte secondary battery accordingto one aspect of the present disclosure includes a belt-like currentcollector, a mixture layer formed on each surface of the currentcollector, and a lead bonded to an exposed portion of the currentcollector where the surfaces of the current collector are exposed, thelead extending from one end of the current collector, the one end andanother end constituting both ends of the current collector in a widthdirection, wherein the mixture layer on at least one surface of thecurrent collector is formed in the width direction and adjacent to theexposed portion on the other end side, and the length in the widthdirection of a portion of the lead disposed on the current collectorranges from 60% to 98% of the width of the current collector.

A non-aqueous electrolyte secondary battery according to one aspect ofthe present disclosure includes a wound electrode assembly manufacturedby winding a positive electrode and a negative electrode with aseparator interposed therebetween, wherein at least one of the positiveelectrode and the negative electrode is constituted by the electrode fora non-aqueous electrolyte secondary battery described above.

Advantageous Effects of Invention

An electrode for a non-aqueous electrolyte secondary battery accordingto one aspect of the present disclosure can be used to provide a woundelectrode assembly in which winding misalignment is sufficiently reducedand with which the decrease in open-circuit voltage (OCV) of the batteryis reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondarybattery according to one embodiment.

FIG. 2 is a perspective view of a wound electrode assembly according toone embodiment.

FIG. 3 includes a front view and a rear view of a positive electrodeaccording to one embodiment.

FIG. 4 is an explanatory view of a method for manufacturing a positiveelectrode according to one embodiment.

FIG. 5 is an explanatory view of a method for manufacturing a positiveelectrode according to one embodiment.

FIG. 6 includes a front view and a rear view of a positive electrodeaccording to another embodiment.

FIG. 7 includes a front view and a rear view of a positive electrodeaccording to another embodiment.

FIG. 8 is a schematic view of a known electrode for a non-aqueouselectrolyte secondary battery.

DESCRIPTION OF EMBODIMENTS

In an electrode for a non-aqueous electrolyte secondary batteryaccording to one aspect of the present disclosure, winding misalignmentof a wound electrode assembly constituted by the electrode is reduced byextending an exposed portion where a surface of a current collector isexposed in the width direction and by adjusting the length of a portionof a lead on the current collector to be 60% or more of the width of thecurrent collector. The lead extends from one end side of the currentcollector in the width direction. In a known electrode 100 illustratedin FIG. 8, exposed portions 102A and 102B where the surfaces of acurrent collector are exposed without being covered with mixture layers103A and 103B are formed on only one end side of a current collector 101in the width direction, and a lead 104 is unevenly bonded to the currentcollector 101 on one end side in the width direction. Because a portionto which the lead 104 is bonded has a larger thickness than the otherportion in the width direction of the current collector 101, in a woundelectrode assembly constituted by the electrode 100, the electrodeassembly bulges locally on one end side in the axial direction, which islikely to cause winding misalignment of the electrode assembly. In anelectrode for a non-aqueous electrolyte secondary battery according toone aspect of the present disclosure, a lead is disposed on the currentcollector so as not to be unevenly disposed on one end side of thecurrent collector in the width direction. This reduces windingmisalignment of an electrode assembly, which can be problematic when theelectrode 100 is used.

In an electrode for a non-aqueous electrolyte secondary batteryaccording to one aspect of the present disclosure, an exposed portion isnot formed over the full width of the electrode, but a mixture layer isformed in the width direction and adjacent to the exposed portion on theother end side. The other end is one of both ends of the currentcollector in the width direction from which a lead is not extended. Thiscan potentially prevent electrically conductive foreign materials fromentering the electrode assembly.

Electrically conductive foreign materials that possibly cause thedecrease in the OCV of a battery are spatters, for example. Spatters mayoccur when a lead extending from a wound electrode assembly is welded toa battery case. In a typical wound electrode assembly constituting acylindrical battery, a positive-electrode lead extends from one side ofthe electrode assembly in the axial direction, and a negative-electrodelead extends from the other side of the electrode assembly in the axialdirection. In this case, although spatters may enter the electrodeassembly through a front edge of a lead disposed on a current collector,a mixture layer formed on a portion of an exposed portion adjacent tothe other end can potentially prevent the spatters from entering theelectrode assembly. In a non-aqueous electrolyte secondary batteryincluding an electrode according to one aspect of the presentdisclosure, therefore, this can reduce the decrease in open-circuitvoltage (OCV) and reduce the occurrence of internal short-circuit causedby electrically conductive foreign materials, such as spatters.

Embodiments of the present disclosure will be described in detail below.

Figures referred in the embodiments are schematically illustrated, andthe specific dimensions of each component should be determined inconsideration of the following description. The term “almost”, as usedherein, means to include, for example, in the context of almost thesame, substantially the same as well as completely the same. The term“end portion” refers to an end of an object and the vicinity thereof.The term “central portion” refers to the center of an object and thevicinity thereof.

One embodiment is a non-aqueous electrolyte secondary battery 10, whichis a cylindrical battery including a cylindrical metallic case. However,a non-aqueous electrolyte secondary battery according to the presentdisclosure is not limited to this. A non-aqueous electrolyte secondarybattery according to the present disclosure may be a prismatic batteryincluding a prismatic metallic case or a laminated battery including aresin sheet exterior, for example.

FIG. 1 is a cross-sectional view of the non-aqueous electrolytesecondary battery 10. FIG. 2 is a perspective view of an electrodeassembly 14 constituting the non-aqueous electrolyte secondary battery10. As illustrated in FIGS. 1 and 2, the non-aqueous electrolytesecondary battery 10 includes a wound electrode assembly 14 and anon-aqueous electrolyte (not shown). The electrode assembly 14 includesa positive electrode 11, a negative electrode 12, and a separator 13.The positive electrode 11 and the negative electrode 12 are wound withthe separator 13 interposed therebetween. The non-aqueous electrolytecontains a non-aqueous solvent and an electrolyte salt dissolved in thenon-aqueous solvent. The non-aqueous electrolyte is not limited to aliquid electrolyte and may be a solid electrolyte containing a gelpolymer. One side of the electrode assembly 14 in the axial direction ishereinafter sometimes referred to as “upper”, and the other side in theaxial direction is sometimes referred to as “lower”.

The positive electrode 11 includes a belt-like positive-electrodecurrent collector 30, a positive-electrode mixture layer 35 formed onthe positive-electrode current collector 30, and a positive-electrodelead 19. The positive-electrode lead 19 is an electrically conductivemember for electrically connecting the positive-electrode currentcollector 30 to a positive-electrode terminal and extends from an upperend of an electrode group. The electrode group refers to the electrodeassembly 14 except leads. In the present embodiment, thepositive-electrode lead 19 is disposed almost midway between the windingstart portion and the winding end portion of the electrode assembly 14.

The negative electrode 12 includes a belt-like negative-electrodecurrent collector 50, a negative-electrode mixture layer 55 formed onthe negative-electrode current collector 50, and a negative-electrodelead 20. The negative-electrode lead 20 is an electrically conductivemember for electrically connecting the negative-electrode currentcollector 50 to a negative-electrode terminal and extends from a lowerend of the electrode group. In the present embodiment, thenegative-electrode lead 20 is disposed on the winding start portion ofthe electrode assembly 14 and on winding end portion of the electrodeassembly 14.

The positive-electrode lead 19 and the negative-electrode lead 20 arebelt-like electrically conductive members with a larger thickness thanthe current collector and the mixture layer. The thickness of each leadis 3 to 30 times the thickness of the current collector, for example,and typically ranges from 50 to 300 μm. Although the constituentmaterial of each lead is not particularly limited, thepositive-electrode lead 19 is preferably composed of an aluminum-basedmetal, and the negative-electrode lead 20 is preferably composed of anickel- or copper-based metal. The number and position of leads are notparticularly limited. For example, the negative-electrode lead 20 may bedisposed on only the winding start portion or the winding end portion ofthe electrode assembly 14.

In the embodiment illustrated in FIG. 1, a case main body 15 and a seal16 constitute a metallic battery case that contains the electrodeassembly 14 and the non-aqueous electrolyte. Insulating plates 17 and 18are disposed on the top and bottom of the electrode assembly 14. Thepositive-electrode lead 19 extends to the seal 16 through a through-holeof the insulating plate 17 and is welded to the bottom of a filter 22,which is a bottom plate of the seal 16. In the non-aqueous electrolytesecondary battery 10, a cap 26, which is a top plate of the seal 16electrically connected to the filter 22, serves as a positive-electrodeterminal. The negative-electrode leads 20 extend to the bottom of thecase main body 15 and are welded to the bottom inner surface of the casemain body 15. In the non-aqueous electrolyte secondary battery 10, thecase main body 15 serves as a negative-electrode terminal.

As described above, the electrode assembly 14 has a winding structure inwhich the positive electrode 11 and the negative electrode 12 are woundwith the separator 13 interposed therebetween. The positive electrode11, the negative electrode 12, and the separator 13 are belt-like andare wound to be stacked in the radial direction of the electrodeassembly 14. In the electrode assembly 14, the longitudinal direction ofeach electrode is the winding direction (the circumferential direction),and the width direction of each electrode is the axial direction.

The case main body 15 is a closed-end cylindrical metallic container. Agasket 27 is disposed between the case main body 15 and the seal 16 andensures the sealing performance of the battery case. The case main body15 has a protrusion 21 for supporting the seal 16. The protrusion 21 isformed by pressing the side surface of the case main body 15 from theoutside, for example. The protrusion 21 is preferably formed circularlyalong the circumferential direction of the case main body 15 andsupports the seal 16 on the top surface thereof.

The seal 16 has a layered structure of the filter 22, a lower valve body23, an insulating member 24, an upper valve body 25, and the cap 26stacked over the electrode assembly 14 in this order. Each member of theseal 16 is discoidal or ring-shaped, for example, and each member exceptthe insulating member 24 is electrically connected to each other. Thelower valve body 23 and the upper valve body 25 are connected to eachother at their central portions. The insulating member 24 is disposedbetween the peripheries of the lower valve body 23 and the upper valvebody 25. If abnormal heat generation increases the internal pressure ofthe battery, the upper valve body 25 expands toward the cap 26 andseparates from the lower valve body 23, thereby breaking the electricalconnection between the upper valve body 25 and the lower valve body 23.A further increase in internal pressure results in the rupture of theupper valve body 25 and causes a gas to be discharged from an opening inthe cap 26.

The structure of the positive electrode 11 will be described in detailbelow with reference to FIG. 3. FIG. 3 includes a front view and a rearview of the positive electrode 11.

As illustrated in FIG. 3, the positive electrode 11 includes thebelt-like positive-electrode current collector 30 and thepositive-electrode mixture layer 35 formed on each surface of thepositive-electrode current collector 30 (see FIG. 2). Thepositive-electrode mixture layers 35 include a positive-electrodemixture layer 35A formed on a first surface of the positive-electrodecurrent collector 30 and a positive-electrode mixture layer 35B formedon a second surface of the positive-electrode current collector 30. Thepositive-electrode mixture layers 35A and 35B have almost the samepattern. In the present specification, the first surface of the currentcollector refers to a surface to which a lead is bonded, and the secondsurface refers to a surface to which no lead is bonded.

The positive electrode 11 has an exposed portion where both surfaces ofthe positive-electrode current collector 30 are exposed. The exposedportion includes an exposed portion 33A disposed on the first surface ofthe positive-electrode current collector 30 and an exposed portion 33Bdisposed on the second surface of the positive-electrode currentcollector 30. The positive electrode 11 further includes thepositive-electrode lead 19, which is bonded to one of the exposedportions 33A and 33B and extends from one end 31 of thepositive-electrode current collector 30 in the width direction. In theembodiment illustrated in FIG. 3, the positive-electrode lead 19 isbonded to the exposed portion 33A on the first surface of thepositive-electrode current collector 30. The exposed portion 33A enablesthe positive-electrode lead 19 to be directly connected to thepositive-electrode current collector 30. Although the details aredescribed later, the length of a portion of the positive-electrode lead19 disposed on the positive-electrode current collector 30 in the widthdirection of the current collector ranges from 60% to 98% of the widthof the positive-electrode current collector 30.

The positive-electrode current collector 30 is a long electricallyconductive member with an almost constant width. The positive-electrodecurrent collector 30 may be made of a sheet of a metal, such asaluminum, or a film including the metal as a surface layer. A suitableexample of the positive-electrode current collector 30 is made of ametal sheet composed mainly of aluminum or an aluminum alloy. Thepositive-electrode current collector 30 has a thickness in the range of5 to 30 μm, for example. The exposed portions 33A and 33B where thesurfaces of the positive-electrode current collector 30 are exposedextend from one end 31 of the positive-electrode current collector 30 inthe width direction and are rectangular in the front and rear views. Thepositive-electrode mixture layers 35A and 35B are preferably almostentirely formed on each surface of the positive-electrode currentcollector 30 except the exposed portions 33A and 33B. Thepositive-electrode mixture layers 35A and 35B contain apositive-electrode active material, an electrically conductive agent,and a binder, for example. The positive electrode 11 can be manufacturedby applying a positive-electrode mixture slurry, which contains apositive-electrode active material, an electrically conductive agent,such as a carbon powder, a binder, such as a fluoropolymer powder, and asolvent, such as N-methyl-2-pyrrolidone (NMP), to the surfaces of thepositive-electrode current collector 30 and by pressing the film. Thepositive-electrode mixture layers 35A and 35B have a thickness in therange of 50 to 100 μm, for example.

The positive-electrode active material may be a lithium-containingtransition metal oxide containing at least one transition metal element,such as Co, Mn, and/or Ni. The lithium-containing transition metal oxideis preferably, but not limited to, a composite oxide represented by thegeneral formula Li_(1+x)MO₂ (wherein −0.2<x≤0.2, and M contains at leastone of Ni, Co, Mn, and Al). The constituents of a first region and asecond region of the positive-electrode mixture layers 35A and 35Bdescribed later may be almost the same or different from each other. Forexample, the constituent ratio may be different between the first regionand the second region.

The exposed portion 33A is a portion to which the positive-electrodelead 19 is to be bonded and is a portion of the first surface of thepositive-electrode current collector 30 where the first surface isexposed without being covered with the positive-electrode mixture layer35A. The exposed portion 33B is a portion of the second surface of thepositive-electrode current collector 30 where the second surface isexposed without being covered with the positive-electrode mixture layer35B. The exposed portion 33B overlaps the exposed portion 33A in thethickness direction of the positive electrode 11 (the positive-electrodecurrent collector 30). If the exposed portion 33A overlaps thepositive-electrode mixture layer 35B, for example, welding of thepositive-electrode lead 19 to the exposed portion 33A may be inhibited.Thus, the exposed portion 33B is disposed opposite the exposed portion33A. The overlap between the exposed portions 33A and 33B preferablyincludes at least the region of the positive-electrode lead 19 on thepositive-electrode current collector 30.

Although the exposed portions 33A and 33B may be formed by forming thepositive-electrode mixture layers 35A and 35B on the entire surfaces ofthe positive-electrode current collector 30 and subsequently removingpart of the mixture layers, the exposed portions 33A and 33B arepreferably formed by intermittent application of the positive-electrodemixture slurry, as described in detail later. This can eliminate themixture layer removal process and reduce the material cost.

Although the exposed portions 33A and 33B may be formed in an endportion of the positive electrode 11 in the longitudinal direction, theexposed portions 33A and 33B are preferably formed in the centralportion of the positive electrode 11 in the longitudinal direction. Forexample, the exposed portions 33A and 33B are disposed at almost equaldistances from each end of the positive electrode 11 in the longitudinaldirection. In this case, because the positive-electrode lead 19 isbonded in the central portion of the positive-electrode currentcollector 30 in the longitudinal direction, the positive electrode 11has improved current collecting performance compared with the case wherethe positive-electrode lead 19 is bonded in an end portion in thelongitudinal direction, thus contributing to increasing the power of thebattery. The first surface of the positive-electrode current collector30 may have a plurality of exposed portions, and a plurality of leadsmay be welded on the first surface.

In the positive electrode 11, the positive-electrode mixture layer isformed on at least one surface of the positive-electrode currentcollector 30 in the width direction of the positive-electrode currentcollector 30 and adjacent to the exposed portion on the other end 32side. The mixture layer formed adjacent to the exposed portion on theother end 32 side can decrease the lower end space of the electrodeassembly 14 made by welding of the positive-electrode lead 19, forexample, and can potentially prevent electrically conductive foreignmaterials from entering the electrode assembly 14.

In the present embodiment, the positive-electrode mixture layer 35A isformed on the first surface of the positive-electrode current collector30 between the other end 32 of the positive-electrode current collector30 and an end 19 t of the positive-electrode lead 19. Thepositive-electrode mixture layer 35B is also formed on the secondsurface of the positive-electrode current collector 30 between the otherend 32 of the positive-electrode current collector 30 and the positioncorresponding to the end 19 t of the positive-electrode lead 19. Thus,the positive-electrode mixture layers 35A and 35B are formed along theexposed portions 33A and 33B, respectively, on the surfaces of thepositive-electrode current collector 30 in the width direction of thecurrent collector. The position corresponding to the end 19 t of thepositive-electrode lead 19 refers to the position overlapping the end 19t on the second surface of the positive-electrode current collector 30in the thickness direction of the positive electrode 11.

In the present specification, the portions of the positive-electrodemixture layers 35A and 35B adjacent to the exposed portions 33A and 33B,respectively, in the width direction of the positive-electrode currentcollector 30 are referred to as second regions 37A and 37B. The portionadjacent to the exposed portion 33A and the second region 37A isreferred to as a first region 36A of the positive-electrode mixturelayer 35A, and the portion adjacent to the exposed portion 33B and thesecond region 37B is referred to as a first region 36B of thepositive-electrode mixture layer 35B.

The exposed portion 33A to which the positive-electrode lead 19 is to bewelded is adjacent to the first region 36A in the longitudinal directionof the positive-electrode current collector 30, and three sides of theexposed portion 33A except one end 31 are surrounded by the first region36A and the second region 37A. The second region 37A may be separatedfrom the first region 36A formed on both sides of the exposed portion33A in the width direction but is preferably in contact with the firstregion 36A. The exposed portion 33B and the second region 37B havebasically the same pattern as the exposed portion 33A and the secondregion 37A, respectively. In the present embodiment, thepositive-electrode mixture layers 35A and 35B are continuously formed onthe end portions on the other end 32 side on both surfaces of thepositive-electrode current collector 30 over the entire length of thepositive-electrode current collector 30.

As described above, the length L₁₉ of the portion of thepositive-electrode lead 19 disposed on the positive-electrode currentcollector 30 in the width direction of the current collector ranges from60% to 98%, preferably 80% to 98%, particularly preferably 80% to 95%,of the width W₃₀ of the positive-electrode current collector 30. Thelength L₁₉ in this range results in suppression of winding misalignmentof the electrode assembly 14 resulting from the large thickness of thepositive-electrode lead 19.

In the second regions 37A and 37B, the lengths L_(37A) and L_(37B) inthe width direction of the positive-electrode current collector 30preferably range from 0.1% to 40% of the width W₃₀ of the currentcollector. The second regions 37A and 37B preferably do not overlap thepositive-electrode lead 19 in the thickness direction of thepositive-electrode current collector 30. In other words, the secondregions 37A and 37B are preferably formed only between the end 19 t ofthe positive-electrode lead 19 or the position corresponding to the end19 t and the other end 32 of the positive-electrode current collector30. For example, when the length L₁₉ of the positive-electrode lead 19ranges from 80% to 98% of the width W₃₀, the lengths L_(37A) and L_(37B)range from 0.1% to 20% of the width W₃₀, that is, approximately 0.5 to 5mm.

In the present embodiment, there is a space between the second region37A and the end 19 t of the positive-electrode lead 19. Thepositive-electrode lead 19 is not disposed over the entire length of theexposed portion 33A, and the length L₁₉ of the positive-electrode lead19 is 60% or more of the width W₃₀ of the positive-electrode currentcollector 30 and is the length at which the positive-electrode lead 19is not in contact with the second region 37A. Thus, the lengths L_(33A)and L_(33B) of the exposed portions 33A and 33B in the width directionof the positive-electrode current collector 30 are longer than thelength L₁₉. The lengths L_(33A) and L_(33B) may range from 1.05 to 1.5times the length L₁₉, for example. The lengths L_(33B) and L_(37B) arealmost the same as the lengths L_(33A) and L_(37A). The widths of theexposed portions 33A and 33B (the lengths in the longitudinal directionof the positive-electrode current collector 30) are preferably close tothe width of the positive-electrode lead 19, for example, slightlylonger than the width of the positive-electrode lead 19, provided thatthe positive-electrode lead 19 can be bonded to the exposed portion 33Awithout any trouble.

Although the second regions 37A and 37B are formed to cover the otherend 32 of the positive-electrode current collector 30, there may be anexposed portion where the surfaces of the current collector are exposedbetween the second regions 37A and 37B and the other end 32. The secondregions 37A and 37B have a thickness in the range of 50 to 100 μm, forexample, which is almost the same as the thickness of the first regions36A and 36B. Alternatively, the second regions 37A and 37B may have asmaller thickness than the first regions 36A and 36B.

In the positive electrode 11, the exposed portions 33A and 33B arecovered with insulating tapes 38A and 38B. The insulating tape 38Acovers not only the positive-electrode lead 19 but also the first region36A and the second region 37A. In the embodiment illustrated in FIG. 3,the exposed portion 33A and the second region 37A are entirely coveredwith the insulating tape 38A. The insulating tape 38B has almost thesame size as the insulating tape 38A and entirely covers the exposedportion 33B and the second region 37B. The insulating tapes 38A and 38Bhave a thickness in the range of 20 to 70 μm, for example.

A method for manufacturing the positive electrode 11 with the abovestructure will be described below with reference to FIGS. 4 and 5. InFIG. 5, for convenience of explanation, positive-electrode mixturelayers 45 and 46 are illustrated in different dot densities. Asillustrated in FIGS. 4 and 5, the positive electrode 11 is manufacturedby sequentially forming the positive-electrode mixture layers 45 and 46on a long current collector 40 and cutting the long current collector 40at cutting positions X and Y. The positive-electrode mixture layers 45and 46 formed on both surfaces of the long current collector 40 serve asthe positive-electrode mixture layers 35A and 35B, and the long currentcollector 40 is cut at the cutting positions X and Y and serves as thepositive-electrode current collector 30.

In the embodiment illustrated in FIGS. 4 and 5, the positive-electrodemixture slurry is intermittently applied to both surfaces of the longcurrent collector 40 except exposed portions 43 and 44 where the currentcollector surfaces are exposed, thereby forming the positive-electrodemixture layer 45. The positive-electrode mixture slurry is then appliedto the exposed portion 44 to form the positive-electrode mixture layer46. The exposed portions 43 extend in the width direction of the longcurrent collector 40 and are disposed at almost regular intervals in thelongitudinal direction of the current collector. The exposed portions 44are formed almost perpendicular to the exposed portions 43 in thelongitudinal direction of the long current collector 40. Thepositive-electrode mixture slurry is applied to the exposed portions 44to form the positive-electrode mixture layer 46, thereby forming thepositive-electrode mixture layer serving as the first regions 36A and36B and the second regions 37A and 37B while leaving exposed portionsserving as the exposed portions 33A and 33B.

The positive electrode 11 is manufactured, for example, by pressing thefilms of the positive-electrode mixture layers 45 and 46 and cutting thelong current collector 40, on which the mixture layers are formed, atthe cutting positions X and Y. In the formation of thepositive-electrode mixture layers 45 and 46, the constituents andthicknesses of the first regions 36A and 36B and the second regions 37Aand 37B are almost equalized by applying the same positive-electrodemixture slurry at the same thickness. The exposed portion 43 has a widthin the range of approximately 5 to 10 mm, for example, which is widerthan the width of the positive-electrode lead 19. The exposed portion 44has a width in the range of approximately 0.5 to 5 mm, for example,depending on the length of the second regions 37A and 37B (the exposedportions 33A and 33B) in the width direction of the current collector.

FIGS. 6 and 7 illustrate positive electrodes 11X and 11Y according toanother embodiment (insulating tapes are not shown). The positiveelectrode 11X illustrated in FIG. 6 is different from the positiveelectrode 11 in that the second region 37B is not formed on the secondsurface of the positive-electrode current collector 30. Thus, in thepositive electrode 11X, the second region 37A of the positive-electrodemixture layer 35A adjacent to the exposed portion 33A in the widthdirection of the current collector is formed only in an end portion onthe other end 32 side of the first surface of the positive-electrodecurrent collector 30 to which the positive-electrode lead 19 is bonded.The positive-electrode mixture layer 35BX does not have the secondregion 37B, and the exposed portion 33BX is formed over the full widthof the positive-electrode current collector 30.

The positive electrode 11Y illustrated in FIG. 7 is different from thepositive electrode 11 in that the second region 37A is not formed on thefirst surface of the positive-electrode current collector 30. Thus, inthe positive electrode 11Y, the second region 37B of thepositive-electrode mixture layer 35B adjacent to the exposed portion 33Bin the width direction of the current collector is formed only in an endportion on the other end 32 side of the second surface of thepositive-electrode current collector 30 to which the positive-electrodelead 19 is not bonded. The positive-electrode mixture layer 35AY doesnot have the second region 37A, and the exposed portion 33AY is formedover the full width of the positive-electrode current collector 30.

Like the positive electrode 11, the negative electrode 12 includes thebelt-like negative-electrode current collector 50 and thenegative-electrode mixture layer 55 formed on both surfaces of thenegative-electrode current collector 50 (see FIG. 2). Thenegative-electrode current collector 50 may be made of a sheet of ametal, such as copper, or a film including the metal as a surface layer.A negative-electrode active material in the negative-electrode mixturelayer 55 may be any material that can reversibly adsorb and desorblithium ions and is preferably a carbon material, such as graphite, ametal that can be alloyed with lithium, such as Si or Sn, or an alloythereof, an oxide, or the like. The negative-electrode mixture layer 55may contain carboxymethylcellulose (CMC) or styrene-butadiene rubber(SBR) as a binder, for example.

The negative electrode 12 includes the negative-electrode lead 20 thatis bonded to one of exposed portions (not shown) where part of eachsurface of the negative-electrode current collector 50 is exposed andthat extends from one end of the negative-electrode current collector 50in the width direction (in the present embodiment, the lower side of theelectrode assembly 14). The negative electrode 12 is larger than thepositive electrode 11 and has an exposed portion at both ends in thelongitudinal direction. The negative-electrode lead 20 is welded to eachexposed portion, for example.

The negative electrode 12 can also have basically the same structure asthe positive electrode 11. The length of a portion of thenegative-electrode lead 20 on the negative-electrode current collector50 in the width direction of the negative-electrode current collector 50ranges from 60% to 98% of the width of the negative-electrode currentcollector 50, for example. In at least one surface of thenegative-electrode current collector 50, the negative-electrode mixturelayer 55 may be formed in the width direction of the current collectorand adjacent to the other end side of the exposed portion (in thepresent embodiment, the upper side of the electrode assembly 14).

EXAMPLES

Although the present disclosure will be further described in thefollowing examples, the present disclosure is not limited to theseexamples.

Example 1 [Preparation of Positive Electrode]

Lithium cobalt oxide, a carbon powder, and a fluoropolymer powder weremixed at a weight ratio of 100:1:1. A proper amount ofN-methyl-2-pyrrolidone was added to the mixture to prepare apositive-electrode mixture slurry. The positive-electrode mixture slurrywas then intermittently applied to both surfaces of a long currentcollector made of aluminum foil 15 μm in thickness, and the film waspressed with a rolling mill to an electrode plate thickness of 140 μm toform a positive-electrode mixture layer. The long current collector thathad the positive-electrode mixture layer on each surface was cut in apredetermined electrode size, and a positive-electrode lead was weldedto an exposed portion on one surface (first surface) of the currentcollector to prepare a positive electrode.

The positive-electrode lead was an aluminum lead 4 mm in width, 67 mm inlength, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 53.1 mm, which corresponds to 90% of the width of thecurrent collector (59 mm).

The slurry was applied twice to each surface of the long currentcollector, four times in total, to form the positive-electrode mixturelayer, as illustrated in FIGS. 4 and 5. In the first application step,the positive-electrode mixture slurry was intermittently applied to onesurface (first surface) of the long current collector except the exposedportion 43 with a width of 7 mm extending in the width direction of thecurrent collector and except the exposed portion 44 with a width of 1 mmextending in the longitudinal direction of the current collector,thereby forming the positive-electrode mixture layer 45 with a width of58 mm. In the second application step, the positive-electrode mixtureslurry was continuously applied to the exposed portion 44 extending inthe longitudinal direction of the current collector to form thepositive-electrode mixture layer 46 with a width of 1 mm. The slurry wasapplied to the other surface (second surface) of the long currentcollector in the same manner as in the first surface to form thepositive-electrode mixture layers 45 and 46, which overlapped themixture layer on the first surface in the thickness direction of theelectrode plate.

The exposed portion in the resulting positive electrode had a length of58 mm in the width direction of the current collector, and the secondregion of the positive-electrode mixture layer formed adjacent to theexposed portion in the width direction of the current collector had alength of 1 mm (approximately 1.7% of the width of the currentcollector) in the width direction. In the positive electrode, theexposed portions and the second regions were entirely covered with apolyimide insulating tape 12 mm in width, 63 mm in length, and 50 μm inthickness.

[Preparation of Negative Electrode]

A natural graphite powder, carboxymethylcellulose (CMC), andstyrene-butadiene rubber (SBR) were mixed at a weight ratio of 100:1:1.A proper amount of water was added to the mixture to prepare anegative-electrode mixture slurry. The negative-electrode mixture slurrywas then intermittently applied to both surfaces of a long currentcollector made of copper foil, and the film was pressed with a rollingmill to an electrode plate thickness of 160 μm to form anegative-electrode mixture layer. The long current collector that hadthe negative-electrode mixture layer on each surface was cut in apredetermined electrode size, and a negative-electrode lead was weldedto an exposed portion to prepare a negative electrode. The exposedportion was formed at both ends of the negative electrode in thelongitudinal direction, and the negative-electrode lead was welded toeach exposed portion. The exposed portion was covered with the polyimideinsulating tape.

[Preparation of Non-Aqueous Electrolyte]

Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at avolume ratio of 30:70. Lithium hexafluorophosphate (LiPFd was dissolvedin the mixed solvent at a concentration of 1 mol/L to prepare anon-aqueous electrolyte.

[Manufacture of Battery]

The positive electrode and the negative electrode were wound with apolyethylene separator interposed therebetween to prepare a woundelectrode assembly. The electrode assembly was placed in a closed-endcylindrical metallic case main body. An upper end of thepositive-electrode lead was welded to a bottom plate of a seal, and alower end of the negative-electrode lead was welded to a bottom innersurface of the case main body. The non-aqueous electrolyte was pouredinto the case main body, and the opening of the case main body washermetically sealed with a seal with a polypropylene gasket interposedtherebetween, thus manufacturing a cylindrical battery. An insulatingplate was disposed on the top and bottom of the electrode group.

Example 2

The positive-electrode lead was an aluminum lead 4 mm in width, 71.7 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 57.8 mm, which corresponds to 98% of the width of thecurrent collector (59 mm). Except for these, a cylindrical battery wasmanufactured in the same manner as in Example 1.

Example 3

The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 35.4 mm, which corresponds to 60% of the width of thecurrent collector (59 mm). Except for these, a cylindrical battery wasmanufactured in the same manner as in Example 1.

Example 4

The positive-electrode mixture slurry was intermittently applied to thesecond surface of the long current collector except the exposed portion43 with a width of 7 mm extending in the width direction of the currentcollector, thereby forming a positive-electrode mixture layer 59 mm inwidth. Except for this, a cylindrical battery was manufactured in thesame manner as in Example 1. The positive electrode in Example 4 isdifferent from the positive electrode in Example 1 in that the secondregion of the positive-electrode mixture layer is not formed on thesecond surface of the positive-electrode current collector (see FIG. 6).

Example 5

The positive-electrode lead was an aluminum lead 4 mm in width, 71.7 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 57.8 mm, which corresponds to 98% of the width of thecurrent collector (59 mm). Except for these, a cylindrical battery wasmanufactured in the same manner as in Example 4.

Example 6

The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 35.4 mm, which corresponds to 60% of the width of thecurrent collector (59 mm). Except for these, a cylindrical battery wasmanufactured in the same manner as in Example 4.

Example 7

The positive-electrode mixture slurry was intermittently applied to thefirst surface of the long current collector except the exposed portion43 with a width of 7 mm extending in the width direction of the currentcollector, thereby forming a positive-electrode mixture layer 59 mm inwidth. Except for this, a cylindrical battery was manufactured in thesame manner as in Example 1. The positive electrode in Example 7 isdifferent from the positive electrode in Example 1 in that the secondregion of the positive-electrode mixture layer is not formed on thefirst surface of the positive-electrode current collector (see FIG. 7).

Example 8

The positive-electrode lead was an aluminum lead 4 mm in width, 71.7 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 57.8 mm, which corresponds to 98% of the width of thecurrent collector (59 mm). Except for these, a cylindrical battery wasmanufactured in the same manner as in Example 7.

Example 9

The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 35.4 mm, which corresponds to 60% of the width of thecurrent collector (59 mm). Except for these, a cylindrical battery wasmanufactured in the same manner as in Example 7.

Comparative Example 1

In the same manner as in Example 1, the slurry was applied twice to eachsurface of the long current collector, four times in total, to form thepositive-electrode mixture layer. In the first application step, thepositive-electrode mixture slurry was intermittently applied to thefirst surface of the long current collector except the exposed portion 7mm in width extending in the width direction of the current collectorand except the exposed portion 45 mm in width extending in thelongitudinal direction of the current collector, thereby forming thepositive-electrode mixture layer 14 mm in width. In the secondapplication step, the positive-electrode mixture slurry was continuouslyapplied to the exposed portion extending in the longitudinal directionof the current collector to form the positive-electrode mixture layer 45mm in width. The slurry was applied to the second surface of the longcurrent collector in the same manner as in the first surface to form thepositive-electrode mixture layers, which overlapped the mixture layer onthe first surface in the thickness direction of the electrode plate.

The positive-electrode lead was an aluminum lead 4 mm in width, 25.7 mmin length, and 150 μm in thickness. The length of a portion of thepositive-electrode lead disposed on the positive-electrode currentcollector was 11.8 mm, which corresponds to 20% of the width of thecurrent collector (59 mm) (see FIG. 8). The length of the exposedportion in the width direction of the current collector was 14 mm. Inthe positive electrode, the exposed portions were entirely covered witha polyimide insulating tape 12 mm in width, 18 mm in length, and 50 μmin thickness. Except for these, a cylindrical battery was manufacturedin the same manner as in Example 1.

Comparative Example 2

A positive-electrode mixture layer was formed such that the length ofthe exposed portion in the width direction of the current collector was31 mm. The length of a portion of the positive-electrode lead disposedon the positive-electrode current collector was 29.5 mm, whichcorresponds to 50% of the width of the current collector (59 mm). Exceptfor these, a cylindrical battery was manufactured in the same manner asin Comparative Example 1. The positive-electrode lead was an aluminumlead 4 mm in width, 43.4 mm in length, and 150 μm in thickness.

Comparative Example 3

The length of a portion of the positive-electrode lead disposed on thepositive-electrode current collector was 29.5 mm, which corresponds to50% of the width of the current collector (59 mm). Except for this, acylindrical battery was manufactured in the same manner as in Example 1.The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mmin length, and 150 μm in thickness.

Comparative Example 4

The second region of the positive-electrode mixture layer was not formedon each surface of the positive-electrode current collector. An exposedportion extending in the width direction of the current collector wasformed over the full width of the electrode plate. Except for these, acylindrical battery was manufactured in the same manner as in Example 1.

The cylindrical batteries according to the examples and comparativeexamples were evaluated for positive-electrode winding misalignment andOCV by the following methods.

[Evaluation of Positive-Electrode Winding Misalignment]

An electrode assembly in a battery case was examined using X-rays. Amisalignment exceeding a predetermined threshold between positive andnegative electrodes was considered to be winding misalignment. The testwas performed on 10,000 batteries. The winding misalignment percentagewas calculated using the following formula.

Winding misalignment percentage (%)=(Number of batteries with windingmisalignment/10,000)×100

[Evaluation of OCV]

A charge-discharge cycle including constant-current charging at 0.3C toa battery voltage of 4.1 V and constant-current discharging at 0.3C to2.5 V was performed three times at 25° C. The battery charged to 4.1 Vwas then left standing at 45° C. for 1 week. The OCV difference (ΔOCV)was calculated from the OCVs of the battery measured before and afterstanding. A battery with ΔOCV beyond 3σ from the average value wasconsidered to have poor OCV. The test was performed on 10,000 batteries.The poor OCV percentage was calculated using the following formula.

Poor OCV percentage (%)=(Number of batteries with poor OCV/10,000)×100

TABLE 1 Length of second region in width direction of current WindingLead collector (mm) misalignment Poor OCV length* First Secondpercentage percentage (%) surface surface (%) (%) Example 1 90 1 1 0.120.02 Example 2 98 1 1 0.13 0.01 Example 3 60 1 1 0.20 0.02 Example 4 901 — 0.12 0.01 Example 5 98 1 — 0.11 0.02 Example 6 60 1 — 0.19 0.02Example 7 90 — 1 0.14 0.02 Example 8 98 — 1 0.11 0.02 Example 9 60 — 10.23 0.03 Comparative 20 45  45  0.72 0.02 example 1 Comparative 50 28 28  0.54 0.03 example 2 Comparative 50 1 1 0.48 0.03 example 3Comparative 90 — — 0.15 0.34 example 4 *The percentage of the length ofa portion of a positive-electrode lead disposed on a positive-electrodecurrent collector relative to the width of the positive-electrodecurrent collector.

Table 1 shows that the winding misalignment percentage of an electrodeassembly was lower in the batteries according to Examples 1 to 9 than inthe batteries according to Comparative Examples 1 to 3. Thus, windingmisalignment of an electrode assembly can be reduced when the length ofa portion of a positive-electrode lead disposed on a current collectoris 60% or more of the width of the current collector and when the leadis disposed so as not to be unevenly disposed on one end side of thecurrent collector in the width direction.

The poor OCV percentage was lower in the batteries according to Examples1 to 9 than in the battery according to Comparative Example 4. Thus, ahigh OCV can be achieved when a mixture layer (a second region) along anexposed portion in the width direction of a current collector is formedin an end portion on the other end side on at least one surface of thecurrent collector in the width direction. The second region canpotentially prevent spatters from entering an electrode assembly when anegative-electrode lead is welded to a case main body and therebyachieve high OCV.

REFERENCE SIGNS LIST

10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12negative electrode, 13 separator, 14 electrode assembly, 15 case mainbody, 16 seal, 17, 18 insulating plate, 19 positive-electrode lead, 20negative-electrode lead, 21 protrusion, 22 filter, 23 lower valve body,24 insulating member, 25 upper valve body, 26 cap, gasket, 30positive-electrode current collector, 31 one end, 32 the other end, 33A,33B exposed portion, 35, 35A, 35B positive-electrode mixture layer, 36A,36B first region, 37A, 37B second region, 38A, 38B insulating tape, 40long current collector, 43, 44 exposed portion, 45, 46positive-electrode mixture layer, 50 negative-electrode currentcollector, 55 negative-electrode mixture layer

1. An electrode for a non-aqueous electrolyte secondary battery,comprising: a belt-like current collector; a mixture layer formed oneach surface of the current collector; and a lead bonded to an exposedportion of the current collector where the surfaces of the currentcollector are exposed, the lead extending from one end of the currentcollector, the one end and another end constituting both ends of thecurrent collector in a width direction, wherein the mixture layer on atleast one surface of the current collector is formed in the widthdirection and adjacent to the exposed portion on the other end side, andthe length in the width direction of a portion of the lead disposed onthe current collector ranges from 60% to 98% of the width of the currentcollector.
 2. The electrode for a non-aqueous electrolyte secondarybattery according to claim 1, wherein the mixture layer on a firstsurface of the current collector to which the lead is bonded is formedin the width direction and adjacent to the exposed portion on the otherend side.
 3. The electrode for a non-aqueous electrolyte secondarybattery according to claim 1, wherein the mixture layer on a secondsurface of the current collector to which the lead is not bonded isformed in the width direction and adjacent to the exposed portion on theother end side.
 4. The electrode for a non-aqueous electrolyte secondarybattery according to claim 1, further comprising: an insulating tapestuck on the lead, wherein the insulating tape is stuck to cover aportion of the mixture layer formed in the width direction and adjacentto the exposed portion on the other end side.
 5. The electrode for anon-aqueous electrolyte secondary battery according to claim 1, whereinthe mixture layer in an end portion on the other end side on at leastone surface of the current collector is continuously formed over theentire length of the current collector.
 6. The electrode for anon-aqueous electrolyte secondary battery according to claim 1, whereina portion of the mixture layer formed in the width direction andadjacent to the exposed portion on the other end side has a length inthe width direction in the range of 0.1% to 40% of the width of thecurrent collector and is formed in the thickness direction of thecurrent collector so as not to overlap the lead.
 7. A non-aqueouselectrolyte secondary battery comprising: a wound electrode assemblymanufactured by winding a positive electrode and a negative electrodewith a separator interposed therebetween, wherein at least one of thepositive electrode and the negative electrode is constituted by theelectrode for a non-aqueous electrolyte secondary battery according toclaim
 1. 8. The non-aqueous electrolyte secondary battery according toclaim 7, wherein the positive electrode is constituted by the electrodefor a non-aqueous electrolyte secondary battery, and the exposed portionis formed in a central portion of the positive electrode in alongitudinal direction.